Cob bathroom – finally the cob!

The one thing with a back-to-front build like this, building the walls last, is that it’s a long time before the building starts to feel like a real building. It’s been worth the wait though. A month ago, we finally started to build the cob walls.

The end of October in Portugal is usually quite mild and we started work in T-shirts and bare feet. By the end, a month later, it was welly boots and several layers of clothing including multiple pairs of gloves. At least building at this time of year means the cob will dry slowly with the minimum of cracking, and hopefully should be dry enough by January’s frosts to avoid damage.

A note on the clay … In most cob construction, the clay subsoil from the site is used. We do have clay subsoil here. Clay is a breakdown product of schist so the soil contains a lot of it. In fact, the subsoil in one part of the quinta contains clay in perfect proportion to build with, needing only the addition of organic material for tensile strength. So why not use the clay from the quinta in the interests of reducing external inputs and embodied energy? The answer to that is that we’re on a mountainside. Bedrock is never far from the surface and a lot of it is the surface. Subsoil depth varies, but is rarely much more than ½ to 1 metre. If we were to excavate enough subsoil to build in cob with, we would need to remove all the subsoil from an area several times the footprint of each building. I didn’t feel this was acceptable. So I bought in a truckload of pure clay from a local brickworks 20km/12 miles away and the sharp sand to mix with it from the local builders’ merchants.

Here is a succession of snapshots from the cob construction. It’s mostly self-explanatory or covered in previous posts.

Cord on the cob!

This was a piece of chestnut hollowed out by a woodpecker and given to a friend for a drum. But it split slightly as it dried so was no use for a drum and he gave it to me. I cut it in two and sandwiched a double-glazed unit (free from the scrapyard) between to make this window.

9 Comments

Mike!! Nice to hear from you! Progress is slow, but steady. Sometimes impatience breaks through, but much less often these days, having seen what happens when quick gets the upper hand. I watch people around me getting stressed out with the daily drama of having to keep on top of their builders every step of the way and still ending up with a job where loads of corners have been cut or things haven’t been thought through, which they then have to live with. It’s not for me. That’s not to say we get it right first time – far from it: I’m still on a steep learning curve and there are invariably things we hadn’t bargained for which show up sooner or later – but generally they show up before the project is complete and it’s not too difficult to rectify. Most importantly, this way is fun! The process itself becomes as much, if not more, enjoyable than the anticipated goal.

Clay, sand, earth and straw. The ratios we used were 1 part wet clay to 1 part earth and 3 parts sand and as much straw as the mix would reasonably hold while still maintaining cohesion. If the clay is wet enough, you don’t need to add any more water. Also that’s pure clay, as opposed to clay subsoil which is often referred to as just ‘clay’ in cob recipes.

your work seems very nice im trying to make a cob house in norht of portugal im already aware there will be a lot of obstacules and aint easy right now getting answer for some of my questions like:

where i can get the clay ?
its easy to get license to build the home? (i know that i have to make the project and delivery to thw town hall and ask request to local authoritys to build it but will be them “smart” and accept it?)
do you know some arquitect that would like to preform the home design?

if you have any answer to my question will be much apreciated your contact

I got the clay from a local brickworks. There are many around here (though most now closed). But I brought in clay because our mountain soils here are not very deep. To build with them I would have had to dig up most of the quinta. You may have good enough subsoil on your site. If you do, then you don’t need to go looking for clay. It doesn’t have to be pure clay to make cob, just a clay-rich subsoil.

I am deliberately staying away from the necessity to have a project to build because of the difficulty and expense. I’m renovating existing buildings and making small temporary single-purpose constructions out of natural materials. If you go the project route, then you’ll need both an architect and an engineer and permissions will very much depend on the attitude of the camara in your locality. It’s enormously variable.

I know of 2 architects who specialise in natural building, though one has just had her second baby so I don’t think she is taking on any work at the moment. You could try contacting Catarina Pinto in Sintra. Her number is 933 291 112 or you can find her on Facebook.